BONDED REPAIR OF METALLIC AIRCRAFT STRUCTURES USING ADVANCED COMPOSITE MATERIALS
ER CHIANG JENG
ER CHIANG JENG
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Abstract
The use of advanced composite materials for bonded repair of metallic aircraft structures offers an attractive alternative to standard repair using fasteners. Bonded repair results in good aerodynamic surface finish and eliminate stress-concentration associated with the use of fasteners. The repair technique also known as 'crack patching’ was first applied on military aircraft. Since then, this state-of-the-art repair technique has gained wide acceptance and has been applied to civil aircraft in recent years. The primary objective of this research programme is to develop and investigate the optimum bonding process. The process is then applied to restore the fatigue performance of a cracked primary aircraft structure. The programme was carried out in three distinct phases. Phase 1 which constitutes the basic knowledge needed for this development involved literature search on the state-of-the-art in bonding technology. The experimental studies carried out in Phase 2 involved the systematic selection of processes and adhesive systems for strength and durability tests. Various parameters involving the combination of surface preparation, adhesive systems and curing cycle were investigated. The results in Phase 2 showed that a simple field surface preparation technique using grit-blasting followed by silane primer is sufficient to achieve a strong and durable bond using a film adhesive, FM 73M. This optimum process was applied in Phase 3 to the simulated upper longeron using boron/epoxy and graphite/epoxy patches for a stress-corrosion problem. The test showed a life improvement of 7.6 times and 2.4 times for the longitudinal and transverse loading specimens respectively. This process was also combined with a force-fit plugged insert for the repair of a structure with fatigue crack. The quantitative fatigue performance of more than 20 times was achieved without failure and with no apparent degradation to the patch.
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1997
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